Low-Density Co-Inoculation with Bradyrhizobium japonicum SAY3-7 and Streptomyces griseoflavus P4 Promotes Plant Growth and Nitrogen Fixation in Soybean Cultivars

Inoculation density has a marked effect on nodulation and N fixation in soybean (Glycine max L.). Therefore, we conducted this study to determine the optimal inoculation density of Bradyhizobium japonicum SAY3-7 (SAY3-7) and Streptomyces griseoflavus P4 (P4) for plant growth, nodulation, and N fixation, and to investigate the effect of co-inoculation on selected soybean cultivars, using the optimal inoculation density. Nitrogen fixation, in terms of an acetylene reduction activity value, was measured using a flame ionization gas chromatograph. In this study, low-density single inoculation with P4 (105 or 106 cells mL-1) was associated with the highest plant biomass, compared with normal- and high-density single inoculation with P4 (107 or 108 cells mL-1). Moreover, low-density single or co-inoculations with SAY3-7 and/or P4 produced the highest nodule biomass and highest nitrogenase activity, compared with single or dual inoculation at other inoculation densities. Therefore, we evaluated low-density co-inoculation with P4 and SAY3-7, at the rate of 105 cells mL-1, on selected soybean cultivars. Low-density co-inoculation increased the plant biomass, compared with un-inoculated plants. The effects of single and co-inoculation on nodulation did not differ significantly for any of the cultivars, except “Yezin-9” in the first experiment and “Shan Seine” in the second experiment. Low-density inoculation with both bacteria increased N fixation by 15% - 75% for seven of the cultivars in the first experiment and by 15% - 39% for three of the cultivars in the second experiment, compared with single inoculation with SAY3-7. Based on the overall results, we concluded that low-density co-inoculation with P4 and SAY3-7 gave improved plant growth and N fixation.

Effects of algal concentration and initial density on the population growth of Diaphanosoma celebensis Stingelin(Crustacea,Cladocera)

The effects of algal concentration and initial density on the population growth of the estuarine cladocera, Diaphanosoma celebensis Stingelin, were evaluated in an indoor experiment. A 2 × 4 layout that included two algal concentrations （Chlorella pyrenoidosa, 1 × 10^6 and 3 ×10^6 cell/mL） and four inoculation densities （100, 200, 300 and 400 ind./L） were established. Diaphanosoma celebensis were reared in 150 mL flasks containing 50 mL of algal medium at 22℃, under salinity of 10 and a photoperiod of 12 h L： 12 h D. The lag phase required to initiate continuous population growth following inoculation was shorter for D. celebensis fed 1 × 10^6 cell/mL and inoculated at 300 or 400 ind./L than that for D. celebensis fed 3 × 10^6 cell/mL and inoculated at 100 or 200 ind./L. However, D. celebensis fed 3 × 10^6 cell/mL and inoculated at 100 or 200 ind./L exhibited longer periods of positive population growth The maximum population densities were 5 875 ± 324, 6 690 ± 691, 7 735 ± 1,121 and 6 365 ± 691 ind./L for D. celebensis fed 1 × 10^6 cell/mL and inoculated at 100, 200, 300 and 400 ind./L, respectively, and 15 070 ± 379, 12 215 ± 648, 11 960±2,551 and 16 130 ± 880 ind./L for D. celebensis fed 3 ×10^6 cell/mL and inoculated at 100, 200, 300 and 400 ind./L, respectively. The average daily increasing rates of population were 0.076 ± 0.001, 0.065 ± 0.002, 0.055 ±0.002 and 0.048 ± 0.003 for D. celebensis fed 1×10^6 cell/mL and inoculated at 100, 200, 300 and 400 ind./L, respectively, and 0.098± 0.001, 0.078 ± 0.002, 0.072 ± 0.003 and 0.067 ± 0.003 forD. celebensis fed 3 × 10^6 cell/mL and inoculated at 100, 200, 300 and 400 ind./L, respectively. The maximum population density and average daily increasing rate of population increased as the algal concentration increased, whereas an increase in the inoculation density led to a linear decrease in the daily increasing rate of population under both algal concentrations. The results of the present experiment indicate that the algal concentration and inoculation density significantly affect population growth of D. celebensis, Furthermore, the results suggest that the optimal algal concentration and inoculation density for the mass culture ofD. celebensis should be 3 × 10^6 cell/mL and 100 ind./L.